Surface Smoothing of Workpieces

ABSTRACT

Apparatus, systems, and methods for processing workpieces are provided. In one example implementation, a fluorine and oxygen plasma-based process can be used to smooth a roughened surface of a silicon and/or a silicon containing structure. The process can include generating species from a process gas using an inductive coupling element in a first chamber. The process can include introducing a fluorine containing gas and an oxygen containing gas with the species to create a mixture. The process can further include exposing the silicon and/or the silicon containing structure to the mixture such that the mixture at least partially etches a roughened portion to leave a smoother surface of the silicon and/or the silicon containing structure.

PRIORITY CLAIM

The present application claims the benefit of priority of U.S.Provisional Application Ser. No. 62/783,517 titled “Surface Smoothing ofWorkpieces,” filed on Dec. 21, 2018, which is incorporated herein byreference. The present application claims the benefit of priority ofU.S. Provisional Application Ser. No. 62/832,055, titled “SurfaceSmoothing of Workpieces,” filed on Apr. 10, 2019, which is incorporatedherein by reference.

FIELD

The present disclosure relates generally to semiconductor processing andmore particularly, surface treatment processes for smoothing a surfaceof a workpiece.

BACKGROUND

The processing of semiconductor workpieces can involve the depositionand removal of different materials layers on a substrate. Devicedimension and materials thickness continue to decrease in semiconductorprocessing with shrinking critical dimensions in semiconductor devices.In advanced device nodes, materials surface properties, such asroughness, and interface integrity become increasingly critical todevice performance

SUMMARY

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

One example aspect of the present disclosure is directed to a method forprocessing a workpiece. The workpiece can include a silicon containinglayer. A surface of the silicon containing layer can include a roughenedportion. The method can include generating species from a process gasusing an inductive coupling element in a first chamber; providing afluorine-containing gas and an oxygen-containing gas into the species togenerate a mixture; and exposing the surface of the silicon containinglayer to the mixture such that the mixture at least partially etches theroughened portion to leave a smoother surface of the silicon containinglayer.

Variations and modifications can be made to example embodiments of thepresent disclosure.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed discussion of embodiments directed to one of ordinary skill inthe art are set forth in the specification, which makes reference to theappended figures, in which:

FIG. 1 depicts an example surface smoothing process on a structureaccording to example embodiments of the present disclosure;

FIG. 2 depicts an example surface smoothing process on a structureaccording to example embodiments of the present disclosure;

FIG. 3 depicts an example surface smoothing process on a structureaccording to example embodiments of the present disclosure;

FIG. 4 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure;

FIG. 5 depicts a flow diagram of an example method according to exampleembodiments of the present disclosure;

FIG. 6 depicts a flow diagram of an example method according to exampleembodiments of the present disclosure;

FIG. 7 depicts example introduction of fluorine containing gas andoxygen containing gas using post-plasma gas injection according toexample embodiments of the present disclosure;

FIG. 8 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure;

FIG. 9 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure; and

FIG. 10 depicts an example surface roughness improvement as a functionof etch amount.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments, one or moreexamples of which are illustrated in the drawings. Each example isprovided by way of explanation of the embodiments, not limitation of thepresent disclosure. In fact, it will be apparent to those skilled in theart that various modifications and variations can be made to theembodiments without departing from the scope or spirit of the presentdisclosure. For instance, features illustrated or described as part ofone embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that aspects of the presentdisclosure cover such modifications and variations.

Example aspects of the present disclosure are directed to methods forprocessing a workpiece to at least partially remove a roughened surfaceon the workpiece to leave a smoother surface. Silicon and/or siliconcontaining structures can sometimes suffer from increased surfaceroughness after etching. For instance, various processes, such asfluorine-containing and/or oxygen-containing chemistry can be used foretching silicon or silicon containing materials (e.g., SiGe). However,some etch processes can leave significant roughness on the materialssurface which can impact interface properties and device performance.

According to example aspects of the present disclosure, a fluorine andoxygen plasma-based process can be used to smooth the roughened surfaceof the silicon and/or silicon containing structure. More particularly, afluorine and oxygen plasma-based process can be used to detail a softtrim by oxidizing and etching the surface layer simultaneously toimprove surface roughness.

In some embodiments, the process can include dissociating an inert gas(e.g., He, Ar, Xe, Ne, etc.) in a plasma chamber (e.g., using aninductively coupled plasma source). The process can include mixing theinert gas with a fluorine-containing gas and an oxygen-containing gas toform fluorine radicals and oxygen radicals. The fluorine radicals andthe oxygen radicals can be exposed to the workpiece for smoothing of asilicon and/or silicon-containing structure or other surface in theworkpiece.

In some embodiments, the fluorine radicals and/or the oxygen radicalscan be generated in the plasma chamber that is separated from aprocessing chamber by a separation grid. The workpiece can be located inthe processing chamber. The radicals generated in the plasma chamber canpass through the separation grid (e.g., as neutral species) for exposureto the workpiece in the processing chamber.

The fluorine radicals and the oxygen radicals can by generated byinducing a plasma from a process gas in the plasma chamber using aninductively coupled plasma source. The process gas can be a mixturecomprising a fluorine containing gas, an oxygen containing gas, and/or acarrier gas. The fluorine containing gas can be, for instance,tetrafluoromethane (CF₄), nitrogen trifluoride (NF₃), or a gas with aformula CF_(x)H_(y) (e.g., x and y are positive integers), etc. Theoxygen containing gas can be, for instance, oxygen (O₂), water vapor(H₂O), or nitrous oxide (N₂O), etc. The carrier gas (also referred to asan insert gas) can be, for instance, helium (He), argon (Ar), xenon(Xe), neon (Ne), nitrogen (N₂), etc.

In some embodiments, the fluorine radicals and/or oxygen radicals can begenerated by injecting fluorine containing gas and/or oxygen containinggas with species excited by a plasma source (e.g., excited inert gasspecies) at a downstream location of the plasma chamber. For instance,the fluorine containing gas and/or the oxygen containing gas can beinjected at or below the separation grid using post plasma gasinjection.

One example application of the process according to example embodimentsof the present disclosure can be performed during direct etching ofsilicon and/or silicon containing structures. For instance, an etchingprocess can be implemented using fluorine-containing, oxygen-containing,and inert gas. The process can leave a smoother surface with anoxidation layer on top of the surface. The oxidation layer can beremoved, for instance, by a wet process, e.g., hydrofluoric acid (HF)dip, or removed by a dry etch process (e.g., plasma based process).

Another example application can be for surface treatment of a roughenedsilicon or silicon containing surface, such as crystalline silicon,polysilicon, or silicon germanium. The roughened surface can be inducedby a previous etch process or deposition process (e.g., wet etch processor a dry etch process). The roughed surface can be treated using aremote plasma (e.g., plasma generated in a remote plasma sourceseparated from a processing chamber by a separation grid). The plasmacan be based on fluorine-containing and/or oxygen-containing gases. Theprocess can mitigate surface roughness with some material loss.

In some embodiments, the materials losses and the smoothing effect usingthe process(s) according to example embodiments of the presentdisclosure can be balanced. For instance, material losses can beincreased to provide a smoother surface. Less material losses can resultin less smoothing effect. As one example, silicon surface roughness canbe reduced by 30% with less silicon loss relative to achieving apristine silicon surface with more material loss.

In some embodiments, the method can include generating fluorine (F),oxygen (O), carbon (C) or nitrogen (N) radicals with some bonds amongthose species. During reaction of the roughed surface with thosespecies, there can also be a surface layer formed with composition(e.g., represented by the formula SiO_(x)F_(y)C_(z), where x, y, z arepositive integers). On the rough surface, a concave area may have athicker formed surface layer while the convex area has a thinner formedsurface layer. With some process time, the concave area can be etchedmore relative to the convex area, making the surface smoother. Theformed surface layer can be easily removed by a wet process like dilutedHF dip and/or removed by a dry etch process. It can also possible toleave at the surface for the next step if the process flow allows.

The above process is an etching process, which removes Si (amorphous Si,poly Si, crystalline Si or SiGe), as well as a deposition process, whichforms SiO_(x)F_(y)C_(z) layers. The layer thickness can be closelyrelated to etch amount, so the roughness improvement comes with a lossof Si materials.

Adjusting the process condition such as the flow ratio of the fluorinecontaining gas, the flow ratio of the oxygen containing gas, plasmapower, process pressure, and/or process temperature can adjust the ratiobetween the amount of material loss and surface smoothness improvement.As a result, the surface smoothing effect can be enhanced by adjustingthose process parameters.

In some embodiments, the surface smoothing is done on a verticalstructure, rather than on a planer surface. For instance, the surfacesmoothing can be implemented on a Si or SiGe Fin structure for FINFETdevices. Smoothing efficiency (and hence also the material loss) on some3D structures need to be same at top and bottom. These can also beenhanced by adjusting the process conditions.

For some applications, the formed surface layer needs to remain on thesurface with high quality. One measure of quality can be the etch ratevs an etch rate for thermal oxide. To improve the quality, processparameters such as flow ratio of the fluorine containing gas, the flowratio of the oxygen containing gas, plasma power, process pressure,and/or process temperature can be tuned.

Example process parameters for one example implementation according toexample embodiments of the present disclosure are provided below:

-   -   Workpiece Temperature: about 100° C. to about 600° C., such as        about 150° C. to about 300° C.;    -   Pressure: about 100 mTorr to about 4 Torr; such as about 400        mTorr to about 800 mTorr;    -   CF₄ Percentage in O₂: about 0.1% to about 5%, such as 0.1% to        about 1%;    -   Plasma Source Power: about 100 W to about 3000 W, such as about        400 W to about 1000 W.

One example aspect of the present disclosure is directed to a method forprocessing a workpiece. The workpiece can include a silicon containinglayer (e.g., crystalline silicon, polysilicon, silicon germanium, or Finstructure for FINFET devices). A surface of the silicon containing layercan include one or more roughened portions. The method can includegenerating species from a process gas using an inductive couplingelement in a first chamber, introducing a fluorine containing gas (e.g.,tetrafluoromethane (CF₄), nitrogen trifluoride (NF₃), or a gas with aformula CF_(x)H_(y), wherein x and y are positive integers) and anoxygen containing gas (e.g., oxygen (O₂), water vapor (H₂O), or nitrousoxide (NO₂)) with the species to create a mixture (e.g., includingfluorine radicals and oxygen radicals), exposing the surface of thesilicon containing layer to the mixture such that the mixture etches theroughened portion to leave a smoother surface of the silicon containinglayer.

In some embodiments, the roughened portion can include a concave areaand a convex area. The concave area can be thicker than the convex area.As used herein, a roughened portion refers to a surface having concaveand convex areas, even at a nanometer scale level. There is norequirement that the surface be intentionally roughened for a surface tobe considered a roughened surface.

The mixture can etch the concave area more than the convex area to leavethe smoother surface of the silicon containing layer. As used herein, asmoother surface results from or is left from a process (e.g., exposureto a mixture) when a surface roughness of the surface is reducedrelative to prior implementation of the process.

In some embodiments, a concentration of the fluorine containing gas inthe oxygen containing gas is in the range of about 0.1% to about 5%. Insome embodiments, the process gas can include an inert gas (alsoreferred to a carrier gas), e.g., helium (He), argon (Ar), xenon (Xe),neon (Ne), nitrogen (N₂). In some embodiments, at least one of thefluorine containing gas and the oxygen containing gas can be part of theprocess gas. For instance, the workpiece can be in a second chamber thatis separated from the first chamber by a separation grid. At least oneof the fluorine containing gas and the oxygen containing gas can beintroduced via a post-plasma gas injection source located at or belowthe separation grid. The at least one of the fluorine containing gas andthe oxygen containing gas can be mixed with the species to create afiltered mixture for exposure to the workpiece.

In some embodiments, the mixture can oxidize and etch the roughenedportion simultaneously to leave the smoother surface. In someembodiments, an oxidation layer can be formed on the smoother surface ofthe silicon containing layer. The method can further include a wetprocess (e.g., HF dip process) or a dry etch process to remove theoxidation layer. In some embodiments, the method can further include adeposition process such that a formed surface layer with a formulaSiO_(x)F_(y)C_(z) where x, y and z are positive integers remains on theworkpiece. In some embodiments, the formed surface layer can be removedby a wet process or by a dry chemical etch process.

One example aspect of the present disclosure is directed to a plasmaprocessing apparatus for processing a workpiece. The plasma processingapparatus can include a processing chamber having a workpiece support.The workpiece support can support the workpiece during plasmaprocessing. The workpiece can include a silicon containing layer. Asurface of the silicon containing layer can include one or moreroughened portions. The plasma processing apparatus can further includea plasma chamber separated from the processing chamber by a separationgrid. The plasma processing apparatus can include an inductive couplingelement to induce a plasma in a process gas in the plasma chamber. Theplasma processing apparatus can include a first gas source injecting afluorine containing gas, and a second gas source injecting an oxygencontaining gas. A mixture generated by mixing the fluorine containinggas and the oxygen containing gas with species generated in the plasmacan pass through the separation grid to etch the one or more roughenedportions to leave a smoother surface of the silicon containing layer.

Example aspects of the present disclosure provide a number of technicaleffects and benefits. For instance, a fluorine and oxygen containingplasma (e.g., an inductively coupled plasma source) can etch one or moreroughened portions of a silicon containing structure layer (e.g., Finstructure for FINFET devices) to leave a smoother surface of the siliconcontaining structure with reduced silicon material loss. As such, asurface roughness of the silicon containing structure can be improvedsuch that interface properties and device performance can be improved.

Aspects of the present disclosure are discussed with reference to a“workpiece” “wafer” or semiconductor wafer for purposes of illustrationand discussion. Those of ordinary skill in the art, using thedisclosures provided herein, will understand that the example aspects ofthe present disclosure can be used in association with any semiconductorsubstrate or other suitable substrate. In addition, the use of the term“about” in conjunction with a numerical value is intended to refer towithin ten percent (10%) of the stated numerical value. A “pedestal”refers to any structure that can be used to support a workpiece.

FIG. 1 depicts an example surface smoothing process on a structure 50according to example embodiments of the present disclosure. Thestructure 50 is a silicon containing structure (e.g., a FIN structure,crystalline silicon, polysilicon, or silicon germanium) with a roughenedsurface 52. The roughened surface 52 can include a convex area 54 and aconcave area 56.

An etching process 60A according to example aspects of the presentdisclosure can be conducted on the structure 50 to remove one or moreportions of the roughened surface 52. Fluorine containing gas (e.g.,tetrafluoromethane (CF₄), nitrogen trifluoride (NF₃), or a gas with aformula CF_(x)H_(y), wherein x and y are positive integers) and oxygencontaining gas (e.g., oxygen (O₂), water vapor (H₂O), or nitrous oxide(NO₂)) are introduced into the etching process 60A. For instance, thefluorine containing gas and oxygen containing gas can be part of aprocess gas. As another example, at least one of the fluorine containinggas and the oxygen containing gas can be introduced via a post-plasmagas injection source. The etching process 60A removes the roughenedsurface 52 and leaves a smoother surface 58. As such, a surfaceroughness can be improved while keeping critical dimension 59 losssmall.

In some embodiments (not shown in FIG. 1), the concave area 56 can bethicker than the convex area 54. The etching process 60A can etch theconcave area 55 more than the convex area 54 to leave the smoothersurface 58 of the structure 50.

FIG. 2 depicts an example surface smoothing process on a structure 50according to example embodiments of the present disclosure. Thestructure 50 is a silicon containing structure with a roughened surface52.

An oxidation and etching process 60B according to example aspects of thepresent disclosure can be conducted on the structure 50 to remove one ormore portions of the roughened surface 52. Fluorine containing gas(e.g., tetrafluoromethane (CF₄), nitrogen trifluoride (NF₃), or a gaswith a formula CF_(x)H_(y), wherein x and y are positive integers) andoxygen containing gas (e.g., oxygen (O₂), water vapor (H₂O), or nitrousoxide (NO₂)) are introduced into the oxidation and etching process 60B.For instance, the fluorine containing gas and oxygen containing gas canbe part of a process gas. As another example, at least one of thefluorine containing gas and the oxygen containing gas can be introducedvia a post-plasma gas injection source. The oxidation and etchingprocess 60B oxidizes and etches the roughened surface 52 simultaneouslyto leave a smoother surface 58 with an oxidation layer topmost.Subsequent to the oxidation and etching process 60B, a wet process or adry etch process 70 is conducted on the structure 50 to remove theoxidation layer 62. As such, a surface roughness can be improved whilekeeping critical dimension 59 loss small.

FIG. 3 depicts an example surface smoothing process on a structure 50according to example embodiments of the present disclosure. Thestructure 50 is a silicon containing structure with a roughened surface52.

An etching and deposition process 60C according to example aspects ofthe present disclosure can be conducted on the structure 50 to removeone or more portions of the roughened surface 52. Fluorine containinggas (e.g., tetrafluoromethane (CF₄), nitrogen trifluoride (NF₃), or agas with a formula CF_(x)H_(y), wherein x and y are positive integers)and oxygen containing gas (e.g., oxygen (O₂), water vapor (H₂O), ornitrous oxide (NO₂)) are introduced into the etching and depositionprocess 60C. For instance, the fluorine containing gas and oxygencontaining gas can be part of a process gas. As another example, atleast one of the fluorine containing gas and the oxygen containing gascan be introduced via a post-plasma gas injection source. The etchingand deposition process 60C etches the roughened surface 52 and depositsa surface layer 64 with a formula SiO_(x)F_(y)C_(z) where x, y and z arepositive integers to leave a smoother surface 58. Subsequent to theetching and deposition process 60C, a wet process or a dry etch process70 is conducted on the structure 50 to remove the surface layer 64. Assuch, a surface roughness can be improved while keeping criticaldimension loss small.

FIG. 4 depicts an example plasma processing apparatus according toexample embodiments of the present disclosure. As illustrated, plasmaprocessing apparatus 100 includes a processing chamber 110 and a plasmachamber 120 that is separated from the processing chamber 110.Processing chamber 110 includes a workpiece support or pedestal 112operable to support a workpiece 114 to be processed, such as asemiconductor wafer. In this example illustration, a plasma is generatedin plasma chamber 120 (i.e., plasma generation region) by an inductivelycoupled plasma source 135 and desired species are channeled from theplasma chamber 120 to the surface of workpiece 114 through a separationgrid assembly 200.

Aspects of the present disclosure are discussed with reference to aninductively coupled plasma source for purposes of illustration anddiscussion. Those of ordinary skill in the art, using the disclosuresprovided herein, will understand that any plasma source (e.g.,inductively coupled plasma source, capacitively coupled plasma source,etc.) can be used without deviating from the scope of the presentdisclosure.

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122, ceiling 124, and separation grid 200define a plasma chamber interior 125. Dielectric side wall 122 can beformed from a dielectric material, such as quartz and/or alumina. Theinductively coupled plasma source 135 can include an induction coil 130disposed adjacent the dielectric side wall 122 about the plasma chamber120. The induction coil 130 is coupled to an RF power generator 134through a suitable matching network 132. Process gases (e.g., a fluorinecontaining gas, an oxygen containing gas, and a carrier gas) can beprovided to the chamber interior from gas supply 150 and annular gasdistribution channel 151 or other suitable gas introduction mechanism.When the induction coil 130 is energized with RF power from the RF powergenerator 134, a plasma can be generated in the plasma chamber 120. In aparticular embodiment, the plasma processing apparatus 100 can includean optional grounded Faraday shield 128 to reduce capacitive coupling ofthe induction coil 130 to the plasma.

As shown in FIG. 4, a separation grid 200 separates the plasma chamber120 from the processing chamber 110. The separation grid 200 can be usedto perform ion filtering from a mixture generated by plasma in theplasma chamber 120 to generate a filtered mixture. The filtered mixturecan be exposed to the workpiece 114 in the processing chamber.

In some embodiments, the separation grid 200 can be a multi-plateseparation grid. For instance, the separation grid 200 can include afirst grid plate 210 and a second grid plate 220 that are spaced apartin parallel relationship to one another. The first grid plate 210 andthe second grid plate 220 can be separated by a distance.

The first grid plate 210 can have a first grid pattern having aplurality of holes. The second grid plate 220 can have a second gridpattern having a plurality of holes. The first grid pattern can be thesame as or different from the second grid pattern. Charged particles canrecombine on the walls in their path through the holes of each gridplate 210, 220 in the separation grid. Neutral species (e.g., radicals)can flow relatively freely through the holes in the first grid plate 210and the second grid plate 220. The size of the holes and thickness ofeach grid plate 210 and 220 can affect transparency for both charged andneutral particles.

In some embodiments, the first grid plate 210 can be made of metal(e.g., aluminum) or other electrically conductive material and/or thesecond grid plate 220 can be made from either an electrically conductivematerial or dielectric material (e.g., quartz, ceramic, etc.). In someembodiments, the first grid plate 210 and/or the second grid plate 220can be made of other materials, such as silicon or silicon carbide. Inthe event a grid plate is made of metal or other electrically conductivematerial, the grid plate can be grounded. In some embodiments, the gridassembly can include a single grid with one grid plate.

As shown in FIG. 4, according to example aspects of the presentdisclosure, the apparatus 100 can include a gas delivery system 150configured to deliver process gas to the plasma chamber 120, forinstance, via gas distribution channel 151 or other distribution system(e.g., showerhead). The gas delivery system can include a plurality offeed gas lines 159. The feed gas lines 159 can be controlled usingvalves and/or mass flow controllers to deliver a desired amount of gasesinto the plasma chamber as process gas. As shown in FIG. 4, the gasdelivery system 150 can include feed gas line(s) for delivery of afluorine containing gas (e.g., tetrafluoromethane (CF₄), nitrogentrifluoride (NF₃), or a gas with a formula CF_(x)H_(y), wherein x and yare positive integers), feed gas line(s) for delivery of an oxygencontaining gas (e.g., oxygen (O₂), water vapor (H₂O), or nitrous oxide(NO₂)), and feed gas line(s) for delivery of an inert gas (e.g., helium(He), argon (Ar), xenon (Xe), neon (Ne), or nitrogen (N₂)). A controlvalve and/or mass flow controller 158 can be used to control a flow rateof each feed gas line to flow a process gas into the plasma chamber 120.

FIG. 5 depicts a flow diagram of an example method (500) according toexample embodiments of the present disclosure. The method (500) will bediscussed with reference to the plasma processing apparatus 100 of FIG.4 by way of example. The method (500) can be implemented in any suitableplasma processing apparatus. FIG. 5 depicts steps performed in aparticular order for purposes of illustration and discussion. Those ofordinary skill in the art, using the disclosures provided herein, willunderstand that various steps of any of the methods described herein canbe omitted, expanded, performed simultaneously, rearranged, and/ormodified in various ways without deviating from the scope of the presentdisclosure. In addition, various steps (not illustrated) can beperformed without deviating from the scope of the present disclosure.

At (510), the method can include placing a workpiece on a workpiecesupport in a processing chamber. For instance, a workpiece 114 can beplaced on a workpiece support 112 in a processing chamber 110. Theworkpiece 114 can include a silicon containing layer having one or moreroughened portions. For instance, a FIN structure 50 includes aroughened surface 52.

At (520), the method can include generating species from a process gasusing an inductive coupling element in a second chamber. For instance, agas delivery system 150 of a plasma processing apparatus 100 can use thefeed gas lines 159 to deliver a process gas into a plasma chamber 120 togenerate the species.

At (530), the method can include introducing a fluorine containing gasand an oxygen containing gas with the species to create a mixture. Insome embodiments, fluorine containing gas and/or an oxygen containinggas can be introduced as part of the process gas. For instance, the gasdelivery system 150 can use the feed gas lines 159 to deliver thefluorine containing gas and the oxygen containing gas into the plasmachamber 120 to create a mixture (e.g., radicals). In some embodiments,the fluorine containing gas and/or the oxygen containing gas can beintroduced via a post-plasma gas injection, as further described inFIGS. 6 and 7.

In some embodiments, a concentration of the fluorine containing gasrelative to the oxygen containing gas is in the range of about 0.1% toabout 5%. For instance, a concentration of CF₄ relative to O₂ is in arange of about 0.1% to about 5%, such as in a range of about 0.1% toabout 1%.

At (540), the method can include exposing the surface of the workpieceto the mixture such that the mixture at least partially etches at leastpartially roughened portion to leave a smoother surface of theworkpiece. For instance, the workpiece 114 can be exposed to the speciesgenerated in the inductively coupled plasma to remove one or moreroughened portions of the workpiece 114.

FIG. 6 depicts a flow diagram of an example method (600) according toexample embodiments of the present disclosure. The method (600) will bediscussed with reference to the plasma processing apparatus 100 of FIG.4 by way of example. The method (600) can be implemented in any suitableplasma processing apparatus. FIG. 6 depicts steps performed in aparticular order for purposes of illustration and discussion. Those ofordinary skill in the art, using the disclosures provided herein, willunderstand that various steps of any of the methods described herein canbe omitted, expanded, performed simultaneously, rearranged, and/ormodified in various ways without deviating from the scope of the presentdisclosure. In addition, various steps (not illustrated) can beperformed without deviating from the scope of the present disclosure.

At (610), the method can include heating a workpiece in a processingchamber. For instance, a workpiece 114 can include a silicon containinglayer having one or more roughened portions. For instance, a FINstructure 50 includes a roughened surface 52. The workpiece 114 can beheated in a processing chamber 110 to a process temperature. Theworkpiece 114 can be heated, for instance, using one or more heatingsystems associated with a workpiece support 112. In some embodiments,the workpiece 114 can be heated to a process temperature in the range ofabout 100° C. to about 600° C., such as about 150° C. to about 300° C.

At (620), the method can include admitting a process gas into a plasmachamber. For instance, a process gas can be admitted into a plasmachamber interior 125 from a gas source 150 via annular gas distributionchannel 151 or other suitable gas introduction mechanism. In someembodiments, the process gas can be an inert gas, such as helium, argon,etc. Other process gases can be used without deviating from the scope ofthe present disclosure.

At (630), the method can include energizing an inductively coupledplasma source to generate a plasma in a plasma chamber. For instance, aninduction coil 130 can be energized with RF energy from RF powergenerator 134 to generate a plasma in the plasma chamber interior 125.

At (640), the method can include filtering one or more ions generated bythe plasma using a separation grid to create a filtered mixture. Thefiltered mixture can include neutral species (e.g., excited inert gasmolecules). In some embodiments, the one or more ions can be filteredusing a separation grid assembly separating the plasma chamber from aprocessing chamber where the workpiece is located. For instance, theseparation grid assembly 200 can be used to filter ions generated by theplasma. The separation grid 200 can have a plurality of holes. Chargedparticles (e.g., ions) can recombine on the walls in their path throughthe plurality of holes. Neutral species (e.g. radicals) can pass throughthe holes.

In some embodiments, the separation grid 200 can be configured to filterions with an efficiency greater than or equal to about 90%, such asgreater than or equal to about 95%. A percentage efficiency for ionfiltering refers to the amount of ions removed from the mixture relativeto the total number of ions in the mixture. For instance, an efficiencyof about 90% indicates that about 90% of the ions are removed duringfiltering. An efficiency of about 95% indicates that about 95% of theions are removed during filtering.

In some embodiments, the separation grid 200 can be a multi-plateseparation grid. The multi-plate separation grid can have multipleseparation grid plates in parallel. The arrangement and alignment ofholes in the grid plate can be selected to provide a desired efficiencyfor ion filtering, such as greater than or equal to about 95%.

For instance, the separation grid 200 can have a first grid plate 210and a second grid plate 220 in parallel relationship with one another.The first grid plate 210 can have a first grid pattern having aplurality of holes. The second grid plate 220 can have a second gridpattern having a plurality of holes. The first grid pattern can be thesame as or different from the second grid pattern. Charged particles(e.g., ions) can recombine on the walls in their path through the holesof each grid plate 210, 220 in the separation grid 200. Neutral species(e.g., radicals) can flow relatively freely through the holes in thefirst grid plate 210 and the second grid plate 220.

At (650), the method can include injecting a fluorine containing gas andan oxygen containing gas into the filtered mixture to generate radicalsfor etching one or more roughened portions of the workpiece. Forinstance, the fluorine containing gas and the oxygen containing gas canbe injected via a post-plasma gas injection system that can be locatedbetween the first grid plate 210 and the second grid plate 220 of theseparation grid 200. The fluorine containing gas and/or the oxygencontaining gas can be injected via a post-plasma gas injection system ata location beneath the separation grid. Example post plasma gasinjection is illustrated in FIG. 7.

At (660), the method can include exposing the workpiece to the filteredmixture in the processing chamber. More particularly, the workpiece 114can be exposed to radicals generated in the plasma and passing throughthe separation grid assembly 200. For instance, the workpiece 114 can beexposed to radicals generated using post plasma gas injection to etchone or more roughened portions of the workpiece to leave a smoothersurface of the workpiece.

FIG. 7 depicts example introduction of fluorine containing gas andoxygen containing gas using post-plasma gas injection according toexample embodiments of the present disclosure. The separation grid 200includes a first grid plate 210 and a second grid plate 220 disposed inparallel relationship. The first grid plate 210 and the second gridplate 220 can provide for ion/UV filtering.

The first grid plate 210 can have a first grid pattern having aplurality of holes. The second grid plate 220 can have a second gridpattern having a plurality of holes. The first grid pattern can be thesame as or different from the second grid pattern. Species 215 from theplasma can be exposed to the separation grid 200. Charged particles(e.g., ions) can recombine on the walls in their path through the holesof each grid plate 210, 220 in the separation grid 200. Neutral speciescan flow relatively freely through the holes in the first grid plate 210and the second grid plate 220.

Subsequent to the second grid plate 220, a gas injection source 230 canbe configured to introduce a fluorine containing gas and an oxygencontaining gas into the species passing through the separation grid 200.A mixture 225 can pass through a third grid plate 235 for exposure tothe workpiece in the processing chamber.

The present example is discussed with reference to a separation gridwith three grid plates for example purposes. Those of ordinary skill inthe art, using the disclosures provided herein, will understand thatmore or fewer grid plates can be used without deviating from the scopeof the present disclosure. In addition, the fluorine containing gas andan oxygen containing gas can be mixed with the species at any point inthe separation grid and/or after the separation grid in the processingchamber. For instance, the gas source 230 can be located between firstgrid plate 210 and second grid plate 220.

FIG. 8 depicts an example plasma processing apparatus 800 according toexample embodiments of the present disclosure. The plasma processingapparatus 800 is similar to the plasma processing apparatus 100 of FIG.4.

More particularly, plasma processing apparatus 800 includes a processingchamber 110 and a plasma chamber 120 that is separated from theprocessing chamber 110. Processing chamber 110 includes a workpiecesupport or pedestal 112 operable to hold a workpiece 114 to beprocessed, such as a semiconductor wafer. In this example illustration,a plasma is generated in plasma chamber 120 (i.e., plasma generationregion) by an inductively coupled plasma source 135 and desired speciesare channeled from the plasma chamber 120 to the surface of substrate114 through a separation grid assembly 200.

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122, ceiling 124, and separation grid 200define a plasma chamber interior 125. Dielectric side wall 122 can beformed from a dielectric material, such as quartz and/or alumina. Theinductively coupled plasma source 135 can include an induction coil 130disposed adjacent the dielectric side wall 122 about the plasma chamber120. The induction coil 130 is coupled to an RF power generator 134through a suitable matching network 132. Process gases (e.g., an inertgas) can be provided to the chamber interior from gas supply 150 andannular gas distribution channel 151 or other suitable gas introductionmechanism. When the induction coil 130 is energized with RF power fromthe RF power generator 134, a plasma can be generated in the plasmachamber 120. In a particular embodiment, the plasma processing apparatus100 can include an optional grounded Faraday shield 128 to reducecapacitive coupling of the induction coil 130 to the plasma.

As shown in FIG. 8, a separation grid 200 separates the plasma chamber120 from the processing chamber 110. The separation grid 200 can be usedto perform ion filtering from a mixture generated by plasma in theplasma chamber 120 to generate a filtered mixture. The filtered mixturecan be exposed to the workpiece 114 in the processing chamber.

In some embodiments, the separation grid 200 can be a multi-plateseparation grid. For instance, the separation grid 200 can include afirst grid plate 210 and a second grid plate 220 that are spaced apartin parallel relationship to one another. The first grid plate 210 andthe second grid plate 220 can be separated by a distance.

The first grid plate 210 can have a first grid pattern having aplurality of holes. The second grid plate 220 can have a second gridpattern having a plurality of holes. The first grid pattern can be thesame as or different from the second grid pattern. Charged particles canrecombine on the walls in their path through the holes of each gridplate 210, 220 in the separation grid. Neutral species (e.g., radicals)can flow relatively freely through the holes in the first grid plate 210and the second grid plate 220. The size of the holes and thickness ofeach grid plate 210 and 220 can affect transparency for both charged andneutral particles.

In some embodiments, the first grid plate 210 can be made of metal(e.g., aluminum) or other electrically conductive material and/or thesecond grid plate 220 can be made from either an electrically conductivematerial or dielectric material (e.g., quartz, ceramic, etc.). In someembodiments, the first grid plate 210 and/or the second grid plate 220can be made of other materials, such as silicon or silicon carbide. Inthe event a grid plate is made of metal or other electrically conductivematerial, the grid plate can be grounded.

The example plasma processing apparatus 800 of FIG. 8 is operable togenerate a first plasma 802 (e.g., a remote plasma) in the plasmachamber 120 and a second plasma 804 (e.g., a direct plasma) in theprocessing chamber 110. The first plasma 802 can be generated by aninductively coupled plasma source. The second plasma 804 can begenerated by, for instance, a capacitively coupled plasma source (e.g.,bias). As used herein, a “remote plasma” refers to a plasma generatedremotely from a workpiece, such as in a plasma chamber separated from aworkpiece by a separation grid. As used herein, a “direct plasma” refersto a plasma that is directly exposed to a workpiece, such as a plasmagenerated in a processing chamber having a pedestal operable to supportthe workpiece.

More particularly, the plasma processing apparatus 800 of FIG. 8includes a bias source having bias electrode 810 in the pedestal 112.The bias electrode 810 can be coupled to an RF power generator 814 via asuitable matching network 812. When the bias electrode 810 is energizedwith RF energy, a second plasma 804 can be generated from a mixture inthe processing chamber 110 for direct exposure to the workpiece 114. Theprocessing chamber 110 can include a gas exhaust port 816 for evacuatinga gas from the processing chamber 110.

As shown in FIG. 8, according to example aspects of the presentdisclosure, the apparatus 100 can include a gas delivery system 150configured to deliver process gas to the plasma chamber 120, forinstance, via gas distribution channel 151 or other distribution system(e.g., showerhead). The gas delivery system can include a plurality offeed gas lines 159. The feed gas lines 159 can be controlled usingvalves and/or mass flow controllers to deliver a desired amount of gasesinto the plasma chamber as process gas. As shown in FIG. 4, the gasdelivery system 150 can include feed gas line(s) for delivery of afluorine containing gas (e.g., tetrafluoromethane (CF₄), nitrogentrifluoride (NF₃), or a gas with a formula CF_(x)H_(y), wherein x and yare positive integers), feed gas line(s) for delivery of an oxygencontaining gas (e.g., oxygen (O₂), water vapor (H₂O), or nitrous oxide(NO₂)), and feed gas line(s) for delivery of an inert gas (e.g., helium(He), argon (Ar), xenon (Xe), neon (Ne), or nitrogen (N₂)). A controlvalve and/or mass flow controller 158 can be used to control a flow rateof each feed gas line to flow a process gas into the plasma chamber 120.

FIG. 9 depicts an example plasma processing apparatus 900 according toexample embodiments of the present disclosure. The plasma processingapparatus 900 is similar to the plasma processing apparatus 100 of FIG.4, and the plasma processing apparatus 800 of FIG. 8.

More particularly, plasma processing apparatus 900 includes a processingchamber 110 and a plasma chamber 120 that is separated from theprocessing chamber 110. Processing chamber 110 includes a substrateholder or pedestal 112 operable to hold a workpiece 114 to be processed,such as a semiconductor wafer. In this example illustration, a plasma isgenerated in plasma chamber 120 (i.e., plasma generation region) by aninductively coupled plasma source 135 and desired species are channeledfrom the plasma chamber 120 to the surface of substrate 114 through aseparation grid assembly 200.

The plasma chamber 120 includes a dielectric side wall 122 and a ceiling124. The dielectric side wall 122, ceiling 124, and separation grid 200define a plasma chamber interior 125. Dielectric side wall 122 can beformed from a dielectric material, such as quartz and/or alumina. Theinductively coupled plasma source 135 can include an induction coil 130disposed adjacent the dielectric side wall 122 about the plasma chamber120. The induction coil 130 is coupled to an RF power generator 134through a suitable matching network 132. Process gas (e.g., an inertgas) can be provided to the chamber interior from gas supply 150 andannular gas distribution channel 151 or other suitable gas introductionmechanism. When the induction coil 130 is energized with RF power fromthe RF power generator 134, a plasma can be generated in the plasmachamber 120. In a particular embodiment, the plasma processing apparatus100 can include an optional grounded Faraday shield 128 to reducecapacitive coupling of the induction coil 130 to the plasma.

As shown in FIG. 9, a separation grid 200 separates the plasma chamber120 from the processing chamber 110. The separation grid 200 can be usedto perform ion filtering from a mixture generated by plasma in theplasma chamber 120 to generate a filtered mixture. The filtered mixturecan be exposed to the workpiece 114 in the processing chamber.

In some embodiments, the separation grid 200 can be a multi-plateseparation grid. For instance, the separation grid 200 can include afirst grid plate 210 and a second grid plate 220 that are spaced apartin parallel relationship to one another. The first grid plate 210 andthe second grid plate 220 can be separated by a distance.

The first grid plate 210 can have a first grid pattern having aplurality of holes. The second grid plate 220 can have a second gridpattern having a plurality of holes. The first grid pattern can be thesame as or different from the second grid pattern. Charged particles canrecombine on the walls in their path through the holes of each gridplate 210, 220 in the separation grid. Neutral species (e.g., radicals)can flow relatively freely through the holes in the first grid plate 210and the second grid plate 220. The size of the holes and thickness ofeach grid plate 210 and 220 can affect transparency for both charged andneutral particles.

In some embodiments, the first grid plate 210 can be made of metal(e.g., aluminum) or other electrically conductive material and/or thesecond grid plate 220 can be made from either an electrically conductivematerial or dielectric material (e.g., quartz, ceramic, etc.). In someembodiments, the first grid plate 210 and/or the second grid plate 220can be made of other materials, such as silicon or silicon carbide. Inthe event a grid plate is made of metal or other electrically conductivematerial, the grid plate can be grounded.

The example plasma processing apparatus 900 of FIG. 9 is operable togenerate a first plasma 902 (e.g., a remote plasma) in the plasmachamber 120 and a second plasma 904 (e.g., a direct plasma) in theprocessing chamber 110. As shown, the plasma processing apparatus 900can include an angled dielectric sidewall 922 that extends from thevertical sidewall 122 associated with the remote plasma chamber 120. Theangled dielectric sidewall 922 can form a part of the processing chamber110.

A second inductive plasma source 935 can be located proximate thedielectric sidewall 922. The second inductive plasma source 935 caninclude an induction coil 910 coupled to an RF generator 914 via asuitable matching network 912. The induction coil 910, when energizedwith RF energy, can induce a direct plasma 904 from a mixture in theprocessing chamber 110. A Faraday shield 928 can be disposed between theinduction coil 910 and the sidewall 922.

The pedestal 112 can be movable in a vertical direction noted as “V.”For instance, the pedestal 112 can include a vertical lift 916 that canbe configured to adjust a distance between the pedestal 112 and theseparation grid assembly 200. As one example, the pedestal 112 can belocated in a first vertical position for processing using the remoteplasma 902. The pedestal 112 can be in a second vertical position forprocessing using the direct plasma 904. The first vertical position canbe closer to the separation grid assembly 200 relative to the secondvertical position.

The plasma processing apparatus 900 of FIG. 9 includes a bias sourcehaving bias electrode 810 in the pedestal 112. The bias electrode 810can be coupled to an RF power generator 814 via a suitable matchingnetwork 812. The processing chamber 110 can include a gas exhaust port816 for evacuating a gas from the processing chamber 110.

As shown in FIG. 9, according to example aspects of the presentdisclosure, the apparatus 100 can include a gas delivery system 150configured to deliver process gas to the plasma chamber 120, forinstance, via gas distribution channel 151 or other distribution system(e.g., showerhead). The gas delivery system can include a plurality offeed gas lines 159. The feed gas lines 159 can be controlled usingvalves and/or mass flow controllers to deliver a desired amount of gasesinto the plasma chamber as process gas. As shown in FIG. 4, the gasdelivery system 150 can include feed gas line(s) for delivery of afluorine containing gas (e.g., tetrafluoromethane (CF₄), nitrogentrifluoride (NF₃), or a gas with a formula CF_(x)H_(y), wherein x and yare positive integers), feed gas line(s) for delivery of an oxygencontaining gas (e.g., oxygen (O₂), water vapor (H₂O), or nitrous oxide(NO₂)), and feed gas line(s) for delivery of an inert gas (e.g., helium(He), argon (Ar), xenon (Xe), neon (Ne), or nitrogen (N₂)). A controlvalve and/or mass flow controller 158 can be used to control a flow rateof each feed gas line to flow a process gas into the plasma chamber 120.

FIG. 10 depicts an example 1000 surface roughness improvement 1020 as afunction of etch amount 1010. As can be seen in FIG. 10, there is acorrelation between the roughness improvement 1020 and the etch amount1010. As the etch amount 1010 increases, the roughness improvement 1020proportionally increases with the etch amount 1010 until the roughnessimprovement 1020 reaches a plateau (e.g., the etch amount 1010 is in arange of about 30 to about 60).

While the present subject matter has been described in detail withrespect to specific example embodiments thereof, it will be appreciatedthat those skilled in the art, upon attaining an understanding of theforegoing may readily produce alterations to, variations of, andequivalents to such embodiments. Accordingly, the scope of the presentdisclosure is by way of example rather than by way of limitation, andthe subject disclosure does not preclude inclusion of suchmodifications, variations and/or additions to the present subject matteras would be readily apparent to one of ordinary skill in the art.

1.-15. (canceled)
 16. A plasma processing apparatus for processing aworkpiece, comprising: a processing chamber having a workpiece support,the workpiece support configured to support the workpiece during plasmaprocessing, wherein the workpiece comprises a silicon containing layer,wherein a surface of the silicon containing layer comprises a roughenedportion; a plasma chamber separated from the processing chamber by aseparation grid; an inductive coupling element configured to induce aplasma using a process gas in the plasma chamber; a first gas sourceinjecting a fluorine containing gas; a second gas source injecting anoxygen containing gas wherein a mixture generated by mixing the fluorinecontaining gas and the oxygen containing gas with species generated inthe plasma pass through the separation grid to at least partially etchthe roughened portion to leave a smoother surface of the siliconcontaining layer.
 17. The plasma processing apparatus of claim 16,wherein the roughened portion comprises a concave area and a convexarea, wherein the concave area is thicker than the convex area, themixture at least partially etches the concave area more than the convexarea to leave the smoother surface of the silicon containing layer. 18.The plasma processing apparatus of claim 16, wherein a concentration ofthe fluorine containing gas in the oxygen containing gas is in the rangeof about 0.1% to about 5%.
 19. The plasma processing apparatus of claim16, wherein the mixture at least partially oxidizes and at leastpartially etches the at least partially roughened portion simultaneouslyto leave the smoother surface.
 20. The plasma processing apparatus ofclaim 16, wherein the smoother surface comprises a material with aformula SiO_(x)F_(y)C_(z), wherein x, y and z are positive integers.